1. Field of the Invention
The present invention relates to a travel path displaying apparatus in which a current location and a path of travel of a running body, such as an automobile, (hereinafter referred to as a vehicle) are displayed on a display screen which has a map previously displayed thereon.
2. Description of the Prior Art
In an attempt to prevent a driver of a vehicle from losing his way in driving, for example in a strange place, off his desired travel path, there has been developed a travel path displaying apparatus including a distance detector for detecting a distance of travel depending upon a running speed of the vehicle and a direction detector for detecting a running direction and an amount of change of direction, from time to time, wherein the current location of the vehicle on X-Y coordinates is successively computed from the respective results of the above-mentioned detections and the location thus computed is memorized and displayed in the form of a constantly changing pattern of continuous point informations on a display screen having a map including roads or the like previously displayed thereon, so that the driver may confirm the current location of his vehicle.
In such a travel path displaying apparatus it is inevitable that some error in displayed position may occur as the vehicle travels, owing to such factors as accuracies of detections when the distance and/or direction detections are effected and such error in displayed position may increase cumulatively as the vehicle advances, so that the current location and the path of travel displayed may come off the correct road on the map. Then the driver cannot judge the location of the road on the map where he is driving.
Heretofore, a method for correcting such error in position on the basis of interrelation between a pattern of roads on the map and a pattern of the path of travel has been proposed. According to this method, in order to find out a road pattern which corresponds to a pattern of path of travel where the vehicle has passed, a few routes which are considered to correspond to the path through which the vehicle has passed are firstly selected from the complicated road pattern in any manner, and then the respective ones of said routes are separately examined as to adaptability to the path of travel. Thus a road having a pattern most resembling the path of travel is assumed to be the one through which the vehicle has passed and the route of travel is displayed on the corresponding portion of road on the map.
Such method of correction has a drawback in the case where a route which is considered to correspond to the path of travel is to be found out on a map including complicatedly connected roads. In such case, a lot of road patterns may be selected in the first stage and, accordingly, the processing for matching the respective ones of the selected road patterns and the pattern of the path of travel of the vehicle requires considerable time. Furthermore, in the case where the vehicle has passed through a road which is not displayed on the map, it is impossible to effect the matching process between the road patterns and the travel path pattern, so that the correction cannot be made. Particularly in a case where the vehicle has passed through a road which is not indicated on the map or the map includes some mistake or deformation of road, it is impossible to effect the matching of patterns, so that the correction of path of travel becomes interrupted.